As a construction of a continuously variable transmission using a sliding key, the pulley construction is known in which a stationary key rotating with a rotary shaft and a movable pulley having a sliding cylinder are engaged each other through the sliding key (Japanese Patent Application Laid-Open No. 8-219258).
With reference to FIGS. 4 and 5, the conventional pulley construction of the continuously variable transmission is described below. FIG. 4 is a half-sectional view showing the pulley construction in the axial direction of the rotary shaft. FIG. 5 is a perspective view showing a main portion of the rotary shaft.
A rotary shaft 4 that is driven by an engine not shown is supported on a body 6 of the continuously variable transmission by bearings 5a, 5b. A stationary pulley 7 is formed integrally with the rotary shaft 4 such that the stationary pulley 7 projects outward from the rotary shaft 4. Grooves 4b are formed concavely into the periphery of a stepped portion 4a formed on the periphery of the rotary shaft 4 such that the grooves 4b are long in the longitudinal direction of the stepped portion 4a and spaced at regular intervals in the circumferential direction thereof. A sliding key 1 is fitted into the groove 4b and engages a movable pulley 8 having a slidable cylindrical portion 8a, such that the movable pulley 8 operates in contact with the stationary pulley 7 or separably therefrom. The sliding key 1 that is fitted into the groove 4b is required mainly to have a rotation-stopping function or a power-transmitting function. The sliding key 1 is also required as an additional function to have a reciprocating function in the axial direction of the rotary shaft 4. Referring to FIG. 4, reference numeral 9 denotes a V-belt spanned between the stationary pulley 7 and the movable pulley 8.
The sliding key 1 is hitherto formed of metal or a material having a low friction coefficient. As the material having a low friction coefficient, a mixture of polyimide resin, polytetrafluoroethylene resin, and graphite or a mixture of polyetherether ketone resin, carbon fiber, and polytetrafluoroethylene resin is used.
However, in the case where the groove into which the sliding key is fitted is made of metal, sliding contact occurs between the metal of the sliding key and that of the groove. Thus, when the sliding key is used in an environment of a high temperature and a high load, the friction resistance of the sliding key becomes large owing to friction-caused seizing of the metals or corrosion. As a result, the sliding key malfunctions or fails. Using a ball spline construction instead of metal leads to a complicated construction and a high cost.
A conventional sliding key made of a resinous material having a low friction coefficient melts, deforms or has a high friction resistance, when it is used in an environment of a high temperature and a high load. Consequently, it is destroyed in a short period of time.
The present invention has been made to overcome the problem. Thus, it is an object of the present invention to provide a sliding key that does not malfunction or fail when it is used in an environment of a high temperature and a high load and also provide a continuously variable transmission using the sliding key.